The following token will be published with a parameter that is the actual token that was registered.
PortableMediator.MediatorTokens.StandardMediatorTokens.TokenRegistered


the following example will write the registered token to the console whenever a new sink is registered:
await mediator.RegisterSubscriber(PortableMediator.MediatorTokens.StandardMediatorTokens.TokenRegistered,
            (object token) =>
            {
                    Console.WriteLine("Token Registered: {0}", token);
            });


The following token will be published whenever a message is published. The parameter will be of type MessagePublishedArgs
PortableMediator.MediatorTokens.StandardMediatorTokens.MessagePublished


the following will write the token, parameter, and the number of subscribers who received the message to the console whenever a mediator message is published:
await mediator.RegisterSubscriber(PortableMediator.MediatorTokens.StandardMediatorTokens.MessagePublished,
                (MessagePublishedArgs args) =>
                {
                    Console.WriteLine("Published Token {0}, with Parameter {1}, {2} times", args.Token, args.Parameter, args.SubscriberCount);
                });